1. Field of the Invention
The present invention relates to a fuel hose having at least a rubber layer and a fluororesin layer formed on the inner surface thereof. The fuel hose of the invention is favorably used, for example, as a fuel hose for automobiles and exhibits excellent performance particularly for alcohol-containing gasoline and sour gasoline.
2. Description of the Related Art
In recent years, control led evaporation of fuel to the air has been demanded in relation to environmental pollution. Therefore, the fuel permeability of the fuel hose for automobiles has been more and more strictly regulated. Conventional fuel hoses prepared only from NBR/PVC have been unable to cope fully with such fuel permeation regulation. Further, the alcohol-containing gasoline used to purify automobile exhaust shows high permeation as compared with gasoline containing no alcohol. A fuel hose having further lower permeability to fuel has therefore been expected. Furthermore, when an automobile is left to stand for a long period of time, the gasoline may be compelled to remain in the gasoline tank for a long time to deteriorate the gasoline. Thus, the fuel hose should have low permeability and high resistance to such deteriorated gasoline (sour gasoline) as well.
The provision of a fluororesin layer excellent in low fuel permeability and resistance to sour gasoline is considered very effective to meet these requirements. However, since fluororesin has poor flexibility and sealing properties at hose joints, a fuel hose formed of a fluororesin layer alone is not suitable. It is thus reasonable to provide a thinned fluororesin layer, preferably as an inner layer of the fuel hose, and a rubber layer as an outer layer thereof. When the fluororesin layer is not provided at end portions of the fuel hose in order to ensure the sealing, it is preferable to impart to the rubber layer characteristics such as the resistance to sour gasoline since the rubber layer at the end portions may contact the gasoline.
The invention disclosed in Japanese Patent Application Laid-Open No. 118549/1996 exemplifies a conventional technique relating to the fuel hose of this kind. In this technique, a rubber layer prepared from epichlorohydrin unvulcanized rubber blended with an organic phosphonium salt and a fluororesin layer formed by extrusion are laminated and subjected to vulcanization.
The invention disclosed in Japanese Patent Application Laid-Open No. 169085/1996 also exemplifies the conventional technique. In this technique, a fluororesin layer is extruded and laminated between an outer rubber layer and an inner rubber layer and then subjected to vulcanization. Th e outer rubber layer is formed of epichlorohydrin unvulcanized rubber blended with a salt of 1,8-diazabicyclo[5,4,0]undecene-7 (DBU salt) and an organic phosphonium salt, and the inner rubber layer is formed of unvulcanized NBR or unvulcanized fluororubber blended with the DBU salt or the organic phosphonium salt.
The invention disclosed in Japanese Patent Application Laid-Open No. 255004/1994 also exemplifies the conventional technique. In this technique, first, the inner surface of a vulcanized rubber tube undergoes a pretreatment for adhesion such as sodium etching treatment, corona discharge treatment, or low-temperature plasma treatment. Subsequently, the inner surface treated undergoes electrostatic coating by use of fluororesin powder, and is heated and cooled to prepare a fuel hose having a fluororesin layer on the inner surface of the rubber tube.
Fluoropolymers in general have a disadvantage of having weak adhesion to rubber materials, and fluororesins in particular are serious in this defect. In preparation of the fuel hose having a rubber layer formed on the outer surface of a thinned fluororesin layer, the adhesion of both layers presents a serious problem.
The aforesaid Japanese Patent Application Laid-Open Nos. 118549/1996 and 169085/1996 relating to the conventional techniques disclose vulcanization adhesion of the fluororesin layer to an unvulcanized rubber layer. That is, they do not disclose a technique allowing adhesion of the fluororesin layer to a rubber layer vulcanized already. When the fluororesin layer and the unvulcanized rubber layer are allowed to adhere by vulcanization, electrostatic powder coating of the fluororesin layer onto the unvulcanized rubber layer is difficult. Therefore, the formation of a good thin fluororesin layer by the electrostatic powder coating is also difficult.
The conventional technique of the aforesaid Japanese Patent Application Laid-Open No. 255004/1994 relates to a technical problem in adhesion of the thinned fluororesin layer to the vulcanized rubber layer. However, means for solving this problem is to perform a pretreatment for adhesion such as sodium etching treatment, corona discharge treatment, and low-temperature plasma treatment to the inner surface of the rubber layer. These pretreatments for adhesion complicate the production process to deteriorate production efficiency and production cost.
It is an object of the present invention to provide a simple and effective means for allowing a thin fluororesin layer to adhere to a vulcanized rubber layer in a fuel hose.
A first aspect of the invention provides a fuel hose comprising a rubber layer and a fluororesin layer adhering to the inner surface thereof, wherein rubber forming the rubber layer contains from 2 to 15 phr (parts per 100 parts of rubber) of a phenol-type resin.
The fuel hose of the first aspect has excellent resistance to fuel and resistance to permeation because of the fluororesin layer formed and particularly shows high reliability for the alcohol-containing gasoline and sour gasoline. Particularly when the innermost layer of the fuel hose is the fluororesin layer, the fuel hose exhibits the resistance to fuel most efficiently.
Since the rubber forming the rubber layer of the fuel hose contains from 2 to 15 phr of the phenol-type resin, adhesion to the fluororesin layer can be ensured without relying upon the vulcanization adhesion. Accordingly, first, the fuel hose can avoid troubles such as blocking of the flow path and reduction in vibration durability of the fuel hose caused by weak adhesion of the rubber layer to the fluororesin layer. Secondly, the formation of the thin fluororesin layer can be satisfactorily performed through the electrostatic powder coating, because it requires no extrusion which is needed in vulcanization adhesion
Furthermore, resin in general tends to deteriorate in resin performance when adhesive agents are added thereto. In the first aspect, the phenol-type resin is added to the rubber forming the rubber layer, and no adhesion agent is added to the fluororesin forming the fluororesin layer, thus to avoid the deterioration in performance of the fluororesin layer.
When the content of the phenol-type resin in the rubber forming the rubber layer is less than 2 phr, adhesion to the fluororesin may be deteriorated, and the resistance of the rubber layer itself to the sour gasoline also tends to become insufficient, particularly when epichlorohydrin rubber is used. The content exceeding 15 phr may invite deterioration in mechanical properties, compression set, and low-temperature properties, although the resistance of the rubber layer itself to the sour gasoline is satisfactorily maintained.
In a second aspect of the invention, the fluororesin is melted and allowed to adhere to the inner surface of the rubber layer by the electrostatic powder coating, and thus the fluororesin layer according to the first aspect is formed.
In the second aspect, a good thin fluororesin layer is formed by the powder coating. Furthermore, the thin fluororesin layer can be formed with ease in an arbitrary form and at an arbitrary portion of the hose. The arbitrary form is, for example, a smooth tubular form, a corrugated form, or a tubular form having a concave portion for containing a seal ring or other concave and/or convex portions. The arbitrary portion of the hose is, for example, the entire inner surface of a tubular rubber layer or the inner surface excluding end portions of the inner surface of the tubular rubber layer.
Since the fluororesin layer can be shaped, for example, into a corrugated form as described above, the flexibility of the fuel hose is ensured with ease. Furthermore, since the fluororesin layer can be formed on the inner surface of the rubber layer excluding the end portions thereof, the sealing at the hose joints can be ensured with ease. Moreover, for example, when the concave portion for containing a seal rubber ring is formed on the end inner surface of the rubber layer, the fluororesin layer can also be formed on the concave portion with ease. Accordingly, the sealing can be ensured with ease while maintaining the low permeability to fuel.
In a third aspect of the invention, the thickness of the fluororesin layer according to the first or second aspect is from 0.05 to 0.5 mm. In the third aspect, the thickness of 0.05 mm or more makes it possible to ensure particularly effectively the resistance to fuel of the fuel hose and resistance to permeation of the fuel. The thickness of 0.5 mm or less makes it possible to ensure particularly fully the flexibility of the fuel hose.
In a fourth aspect of the invention, the phenol-type resins according to the first to third aspects are at lest one resin selected from the group consisting of a resol-type phenol resin, a novolak-type phenol resin, a resorcin resin, a resorcin-modified phenol resin, a cresol resin, a cresol-modified phenol resin, a terminal-modified p-alkylphenol-formaldehyde resin, a non-thermal reaction alkylphenol resin, a thermal reaction phenol resin, a cashew-modified phenol resin, an aromatic hydrocarbon resin-modified phenol resin, a melamine-modified phenol resin, an oil-modified phenol resin, a terpene-modified phenol resin, and a furan-modified phenol resin.
The phenol-type resins in the forth aspect are preferably used as phenol-type resins to be added to the rubber forming the rubber layer, and particularly the cashew-modified phenol resin is preferable.
In a fifth aspect of the invention, the phenol-type resins according to the first to third aspects are resins represented by the following formula (1). In formula (1), R represents a hydrocarbon group, and n is a positive integer. Formula (1) 
The phenol-type resins represented by formula (1) of the fifth aspect are particularly preferred as the phenol-type resins to be added to the rubber forming the rubber layer.
In a sixth aspect of the invention, the rubber forming the rubber layer according to the first to fifth aspects is NBR-PVC (blend of acrylonitrile-butadiene rubber with polyvinyl chloride), epichlorohydrin rubber, NBR (acrylonitrile-butadiene rubber), binary or ternary FKM (fluororubber), CPE (chlorinated polyethylene rubber), or CSM (chlorosulfonated polyethylene rubber).
The rubbers shown in the sixth aspect are preferable examples of the rubber forming the rubber layer of the fuel hose. Of the rubber, the epichlorohydrin rubber, which has ether linkages in the main chain, undergoes cleavage by peroxides with ease to cause softening and deterioration. Accordingly, the rubber inherently has very low resistance to deteriorated fuel (sour gasoline), but the resistance to sour gasoline has been remarkably improved by blending the phenol-type resins as described above.
In a seventh aspect of the invention, the fluororesin forming the fluororesin layer according to the first to sixth aspects is a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE).
The powder of the fluororesin consisting of the copolymer of VDF and CTFE melts at a temperature that causes no thermal deterioration of the rubber layer. Furthermore, the rigidity of the fluororesin layer formed by melting the powder is not so high. Accordingly, the formation of the fluororesin layer by the electrostatic powder coating allows the rubber layer to avoid thermal deterioration and in addition allows the fuel hose to maintain flexibility.
In an eighth aspect of the invention, the VDF/CTFE molar ratio in the copolymer according to the seventh aspect is from 98/2 to 85/15. The fluororesin powder of these VDF/CTFE molar ratios has a low melting temperature and can maintain the flexibility of the fluororesin layer with ease. The VDF molar ratio exceeding the above range results in raising excessively the melting temperature of the fluororesin and results in an increase of the rigidity of the fluororesin layer. Contrarily, the VDF molar ratio not reaching the above range causes excessive reduction in the melting temperature of the fluororesin relative to the temperature of the fuel hose in use, and invites deterioration in resistance to gasoline permeation.
The above and other advantages of the invention will become more apparent from the following description and the accompanying drawing.